The present invention relates to the field of wired communication systems, and, more specifically, to the networking of devices using telephone lines.
FIG. 1 shows the wiring configuration for a prior-art telephone system 10 for a residence or other building, wired with a telephone line 5. Residence telephone line 5 consists of single wire pair which connects to a junction-box 16, which in turn connects to a Public Switched Telephone Network (PSTN) 18 via a cable 17, terminating in a public switch 19, apparatus which establishes and enables telephony from one telephone to another. The term xe2x80x9canalog telephonyxe2x80x9d herein denotes traditional analog low-frequency audio voice signals typically under 3 KHz, sometimes referred to as xe2x80x9cPOTSxe2x80x9d (xe2x80x9cplain old telephone servicexe2x80x9d), whereas the term xe2x80x9ctelephonyxe2x80x9d in general denotes any kind of telephone service, including digital service such as Integrated Services Digital Network (ISDN). The term xe2x80x9chigh-frequencyxe2x80x9d herein denotes any frequency substantially above such analog telephony audio frequencies, such as that used for data. ISDN typically uses frequencies not exceeding 100 KHz (typically the energy is concentrated around 40 KHz). The term xe2x80x9ctelephone devicexe2x80x9d herein denotes, without limitation, any apparatus for telephony (including both analog telephony and ISDN), as well as any device using telephony signals, such as fax, voice-modem, and so forth.
Junction box 16 is used to separate the in-home circuitry from the PSTN and is used as a test facility for troubleshooting as well as for wiring new telephone outlets in the home. A plurality of telephones 13a, 13b, and 13c connects to telephone line 5 via a plurality of outlets 11a, 11b, 11c, and 11d. Each outlet has a connector (often referred to as a xe2x80x9cjackxe2x80x9d), denoted in FIG. 1 as 12a, 12b, 12c, and 12d, respectively. Each outlet may be connected to a telephone via a connector (often referred to as a xe2x80x9cplugxe2x80x9d), denoted in FIG. 1 (for the three telephone illustrated) as 14a, 14b, and 14c, respectively. It is also important to note that lines 5a, 5b, 5c, 5d, and 5e are electrically the same paired conductors.
There is a requirement for using the existing telephone infrastructure for both telephone and data networking. This would simplify the task of establishing a new local area network in a home or other building, because there would be no additional wires and outlets to install. U.S. Pat. No. 4,766,402 to Crane (hereinafter referred to as xe2x80x9cCranexe2x80x9d) teaches a way to form a LAN over two wire telephone lines, but without the telephone service.
The concept of frequency domain/division multiplexing (FDM) is well-known in the art, and provides a means of splitting the bandwidth carried by a wire into a low-frequency band capable of carrying an analog telephony signal and a high-frequency band capable of carrying data communication or other signals. Such a mechanism is described for example in U.S. Pat. No. 4,785,448 to Reichert et al (hereinafter referred to as xe2x80x9cReichertxe2x80x9d). Also is widely used are XDSL systems, primarily Asymmetric Digital Subscriber Loop (ADSL) systems.
Relevant prior art in this field is also disclosed in U.S. Pat. No. 5,896,443 to Dichter (hereinafter referred to as xe2x80x9cDichterxe2x80x9d). Dichter is the first to suggest a method and apparatus for applying such a technique for residence telephone wiring, enabling simultaneously carrying telephone and data communication signals. The Dichter network is illustrated in FIG. 2, which shows a network 20 serving both telephones and a local area network. Data Terminal Equipment (DTE) units 24a, 24b and 24c are connected to the local area network via Data Communication Equipment (DCE) units 23a, 23b and 23c, respectively. Examples of Data Communication Equipment include modems, line drivers, line receivers, and transceivers. DCE units 23a, 23b and 23c are respectively connected to high pass filters (HPF) 22a, 22b and 22c. The HPF""s allow the DCE units access to the high-frequency band carried by telephone line 5. In a first embodiment (not shown in FIG. 2), telephones 13a, 13b and 13c are directly connected to telephone line 5 via connectors 14a, 14b and 14c, respectively. However, in order to avoid interference to the data network caused by the telephones, a second embodiment is suggested (shown in FIG. 2), wherein low pass filters (LPF""s) 21a, 21b and 21c are added to isolate telephones 13a, 13b and 13c from telephone line 5. Furthermore, a low pass filter must also be connected to Junction-Box 16, in order to filter noises induced from or to the PSTN wiring 17. As is the case in FIG. 1, it is important to note that lines 5a, 5b, 5c, 5d and 5e are electrically the same paired conductors.
The Dichter network suffers from degraded data communication performance, because of the following drawbacks:
1. Induced noise in the band used by the data communication network is distributed throughout the network. The telephone line within a building serves as a long antenna, receiving electro-magnetic noise produced from outside the building or by local equipment such as air-conditioning systems, appliances, and so forth. Electrical noise in the frequency band used by the data communication network can be induced in the extremities of the telephone line 5 (line 5e or 5a in FIG. 2) and propagated via the telephone line 5 throughout the whole system. This is liable to cause errors in the data transportation.
2. The wiring media consists of a single long wire (telephone line 5). In order to ensure a proper impedance match to this transmission-line, it is necessary to install terminators at each end of the telephone line 5. One of the advantages of using the telephone infrastructure for a data network, however, is to avoid replacing the internal wiring. Thus, either such terminators must be installed at additional cost, or suffer the performance problems associated with an impedance mismatch.
3. In the case where LPF 21 is not fitted to the telephones 13, each connected telephone appears as a non-terminated stub, and this is liable to cause undesirable signal reflections.
4. In one embodiment, an LPF 21 is to be attached to each telephone 13. In such a configuration, an additional modification to the telephone itself is required. This further makes the implementation of such system complex and costly, and defeats the purpose of using an existing telephone line and telephone sets xe2x80x98as isxe2x80x99 for a data network.
5. The data communication network used in the Dichter network supports only the xe2x80x98busxe2x80x99 type of data communication network, wherein all devices share the same physical media. Such topology suffers from a number of drawbacks, as described in U.S. Pat. No. 5,841,360 to the present inventor, which is incorporated by reference for all purposes as if fully set forth herein. Dichter also discloses drawbacks of the bus topology, including the need for bus mastering and logic to contend with the data packet collision problem. Topologies that are preferable to the bus topology include the Token-Ring (IEEE 803), the PSIC network according to U.S. Pat. No. 5,841,360, and other point-to-point networks known in the art (such as a serial point-to-point xe2x80x98daisy chainxe2x80x99 network). Such networks are in most cases superior to xe2x80x98busxe2x80x99 topology systems.
The above drawbacks affect the data communication performance of the Dichter network, and therefore limit the total distance and the maximum data rate such a network can support. In addition, the Dichter network typically requires a complex and therefore costly transceiver to support the data communication system. While the Reichert network relies on a star topology and does not suffer from these drawbacks of the bus topology, the star topology also has disadvantages. First, the star topology requires a complex and costly hub module, whose capacity limits the capacity of the network. Furthermore, the star configuration requires that there exist wiring from every device on the network to a central location, where the hub module is situated. This may be impractical and/or expensive to achieve, especially in the case where the wiring of an existing telephone system is to be utilized. The Reichert network is intended for use only in offices where a central telephone connection point already exists. Moreover, the Reichert network requires a separate telephone line for each separate telephone device, and this, too, may be impractical and/or expensive to achieve.
There is thus a widely-recognized need for, and it would be highly advantageous to have, a means for implementing a data communication network using existing telephone lines of arbitrary topology, which continues to support analog telephony while also allowing for improved communication characteristics by supporting a point-to-point topology network.
The present invention provides a method and apparatus for using the telephone line wiring system within residence or other building for both analog telephony service and a local area data network featuring a serial xe2x80x9cdaisy chainedxe2x80x9d or other arbitrary topology. First, the regular outlets are modified or substituted to allow splitting of the telephone line having two wires into segments such that each segment connecting two outlets is fully separated from all other segments. Each segment has two ends, to which various devices, other segments, and so forth, may be connected. A low pass filter is connected in series to each end of the segment, thereby forming a low-frequency path between the external ports of the low pass filters, utilizing the low-frequency band. Similarly, a high pass filter is connected in series to each end of the segment, thereby forming a high-frequency path between the external ports of the high pass filters, utilizing the high-frequency band. The bandwidth carried by the segments is thereby split into non-overlapping frequency bands, and the distinct paths can be interconnected via the high pass filters and low pass filters as coupling and isolating devices to form different paths. Depending on how the devices and paths are selectively connected, these paths may be simultaneously different for different frequencies. A low-frequency band is allocated to regular telephone service (analog telephony), while a high-frequency band is allocated to the data communication network. In the low-frequency (analog telephony) band, the wiring composed of the coupled low-frequency paths appears as a normal telephone line, in such a way that the low-frequency (analog telephony) band is coupled among all the segments and is accessible to telephone devices at any outlet, whereas the segments may remain individually isolated in the high-frequency (data) band, so that in this data band the communication media, if desired, can appear to be point-to-point (such as a serialized xe2x80x9cdaisy chainxe2x80x9d) from one outlet to the next. The term xe2x80x9clow pass filterxe2x80x9d herein denotes any device that passes signals in the low-frequency (analog telephony) band but blocks signals in the high-frequency (data) band. Conversely, the term xe2x80x9chigh pass filterxe2x80x9d herein denotes any device that passes signals in the high-frequency (data) band but blocks signals in the low-frequency (analog telephony) band. The term xe2x80x9cdata devicexe2x80x9d herein denotes any apparatus that handles digital data, including without limitation modems, transceivers, Data Communication Equipment, and Data Terminal Equipment.
A network according to the present invention allows the telephone devices to be connected as in a normal telephone installation (i.e., in parallel over the telephone lines), but can be configured to virtually any desired topology for data transport and distribution, as determined by the available existing telephone line wiring and without being constrained to any predetermined data network topology. Moreover, such a network offers the potential for the improved data transport and distribution performance of a point-to-point network topology, while still allowing a bus-type data network topology in all or part of the network if desired. This is in contrast to the prior art, which constrains the network topology to a predetermined type.
A network according to the present invention may be used advantageously when connected to external systems and networks, such as xDSL, ADSL, as well as the Internet.
In a first embodiment, the high pass filters are connected in such a way to create a virtual xe2x80x98busxe2x80x99 topology for the high-frequency band, allowing for a local area network based on DCE units or transceivers connected to the segments via the high pass filters. In a second embodiment, each segment end is connected to a dedicated modem, hence offering a serial point-to-point daisy chain network. In all embodiments of the present invention, DTE units or other devices connected to the DCE units can communicate over the telephone line without interfering with, or being affected by, simultaneous analog telephony service. Unlike prior-art networks, the topology of a network according to the present invention is not constrained to a particular network topology determined in advance, but can be adapted to the configuration of an existing telephone line installation. Moreover, embodiments of the present invention that feature point-to-point data network topologies exhibit the superior performance characteristics that such topologies offer over the bus network topologies of the prior art, such as the Dichter network and the Crane network.
Therefore, according to the present invention there is provided a network for telephony and data communication including: (a) at least one electrically-conductive segment containing at least two distinct electrical conductors operative to conducting a low-frequency telephony band and at least one high-frequency data band, each of the segments having a respective first end and a respective second end; (b) a first low pass filter connected in series to the respective first end of each of the segments, for establishing a low-frequency path for the low-frequency telephony band; (c) a second low pass filter connected in series to the respective second end of each of the segments, for establishing a low-frequency path for the low-frequency telephony band; (d) a first high pass filter connected in series to the respective first end of each of the segments, for establishing a high-frequency path for the at least one high-frequency data band; (e) a second high pass filter connected in series to the respective second end of each of the segments, for establishing a high-frequency path for the at least one high-frequency data band; and (f) at least two outlets each operative to connecting at least one telephone device to at least one of the low-frequency paths, and at least two of the at least two outlets being operative to connecting at least one data device to at least one of the high-frequency paths; wherein each of the segments electrically connects two of the outlets; and each of the outlets that is connected to more than one of the segments couples the low-frequency telephony band among each of the connected segments.